Froude Krylov Moment

- January 18, 2024 at 12:04 pm
  
  w.s.syafruddin2
  Subscriber
  
  Hello..
  Since there is no amplitude parameter input in hydrodynamic diffraction, how do I obtain the wave amplitude of the Foude-Krylov moment?
- January 19, 2024 at 2:07 pm
  
  Shuangxing Du
  Ansys Employee
  
  The ordinate title of the graph indicates that it is the amplitude of the moment (of the Froude-Krylov wave about x-axis in the wave direction 90 degrees) per unit incident wave amplitude.
- January 19, 2024 at 3:33 pm
  
  w.s.syafruddin2
  Subscriber
  
  Many thanks for reply @sxdu
  Okay, Do you know how to obtain only the froude-krylov moment? in case I don't know the incident wave amplitude
- January 19, 2024 at 4:12 pm
  
  Shuangxing Du
  Ansys Employee
  
  Can you explain what you want to have? The above graph gives the amplitude of the Froude-Krylov moment about x-axis due to the incident wave with the amplitude of 1 meter at the incident wave direction of 90 degrees for each incident wave direction.
- January 19, 2024 at 5:33 pm
  
  w.s.syafruddin2
  Subscriber
  
  Thanks for reply @sxdu
  I just want to have froude-Krylov moment (N.m) not FK moment per unit amplitude (N.m/m)
- January 22, 2024 at 9:12 am
  
  Shuangxing Du
  Ansys Employee
  
  As the incident wave parameters (such as wave amplitude, wave direction and wave frequency) are known when you do the analysis, the Froude-Krylov moment (N.m) is the Froude-Frylov moment RAO (in the unit of N.m/m shown in your graph) timing the known incident wave amplitude.
- January 22, 2024 at 11:59 am
  
  w.s.syafruddin2
  Subscriber
  
  The graph is obtained from hydrodynamic diffraction analysis, not hydrodynamic response, so there's no wave amplitude input.
  Anyway, could you provide the equation used in calculating the Froude-Krylov moment in Ansys?
- January 22, 2024 at 12:28 pm
  
  Shuangxing Du
  Ansys Employee
  
  For a time domain hydrodynamic response in irrgular waves, the irrgular waves are represented by the summation of the large number of wave components (including wave amplitude, frequency, direction, phase, see Aqwa Theory Manual, Section 2.1.2). The wave exciting force (summation of the Froude-Krylov force and the diffraction force) is given in the Aqwa thoery manual, equation 13.28
  The amplitude of in the above eqaution is the amplitude of Froude-Krylov foroce/moment RAO displayed in your graph. The phase of Froude-Krylov force/moment RAO will also be used in the above equation.